Reducing power consumption is an important concern with many modern personal computers. The reduction of power consumption is particularly significant with respect to battery-powered, laptop or notebook style personal computers. Currently, one method of reducing power consumption being attempted is lowering the power supply voltage of the computer system itself. However, some problems arise when lowering the operating potential of the computer system.
One of the problems with lowering the operating potential of the computer system is that some of the peripheral devices which may be coupled to the computer system through some type of interface or bus are only operable at the original higher potential. For example, a peripheral for a 5 volt computer system may not operate correctly in a 3.3 volt computer system. However, the computer system users still desire the use of these 5 volt peripheral devices. Therefore, it is desirable to have a computer system that operates at a lower power supply potential, yet be able to utilize peripherals which are rated to operate at another power supply potential.
Computer systems operate in conjunction with numerous peripheral devices. In the prior art, these peripheral devices usually operate at the same voltage as the computer system. However, if a computer system is set to operate at one voltage and the peripherals operate at another voltage then separate voltage translation circuitry is required such that any signals transferred between the two can be compatible. The additional voltage translation circuitry required to convert signals of different operating potentials between the peripheral devices and the computer system is expensive and requires adjustments in the timing delays of the system. Thus, it is desirable to have a computer system in which peripherals can operate at one operating potential and be coupled to and operate with the remainder of the computer system without the need for separate voltage translation circuitry.
In notebook computer systems, since the primary basis is on conserving power, if the computer system can operate at a lower voltage, then the computer system would incur less power consumption. Therefore, it is desirable that in a computer system that operates at multiple operating potentials, that it operate at the lowest of these potentials as often as possible in order to conserve power. However, if the system is capable of operating at multiple power supply potentials and is coupled to an interface which only operates at one power supply potential, it is desirable to have computer systems which is capable of operating at that potential when the interface is coupled to the computer system. Therefore, it is desirable to have a computer system which operates at its lowest potential when not coupled to an interlace of another power supply potential and which operates at the potential of the interface when one such interface is coupled to the computer system.
Moreover, if an interface which is operating at one power supply potential is coupled to a computer system operating at a different power supply potential, the computer system typically must be powered down. That is, the computer system must be turned off to allow the interface to be coupled to the computer system. In order to resume the operation of the computer system, the computer system must be rebooted and must execute a power-up routine. These requirements of powering on and off the system produce timing delays in the system. Therefore, it is desirable to have a computer system which does not have to be powered down (i.e., have the power turned off) when attaching an interface which operates at a different power supply potential.
As will be shown, the present invention provides a computer system which is capable of operating with peripheral devices at another operating potential. The present invention facilitates this by providing an interface bus which is capable of switching between multiple power supply operating potentials. The present invention also provides a method and apparatus for allowing an interface to be coupled to a computer system without having to fully power down the computer system.